1. Field of the Invention
This invention relates to constant-speed vertical-axis centrifugal pumps and, more particularly, a device for regulating the pumping capacity of said pumps. The present application claims priority under 35 U.S.C. .sctn.119 to Swiss Application No. 0052/99, which is herein incorporated by reference.
2. Brief Description of the Prior Art
In pumping systems where the volume of water to be transported fluctuates, such as with municipal waste water or rain water, there is a simple device that adapts a pumping capacity to a current volume of fluid to be pumped by means of an appropriate change in the shape of a pumping pit, without any variation in the speed of the pump.
One such prior art device is described in CH 533,242 and CH 580,229. The device consists of an open cylinder which is located in the pumping pit. Above the bottom of the cylinder there is a tangential inlet that corresponds to the direction of rotation of a pump extending into the cylinder. A suction pipe is connected to the suction side of the pump.
If the volume of water in the pit is great enough that the water level rises above the edge of the cylinder, the water flows over the edge of the cylinder, into the cylinder, and directly to the pump suction tube, without any significant difference between the levels inside and outside the cylinder. The pump thereby achieves its full pumping capacity. If the volume of water inside the pit decreases, less and less water can flow over the edge of the cylinder, and the water level inside the cylinder becomes lower than the level outside the cylinder. Consequently, more and more water flows through the tangential inlet opening into the cylinder and generates a rotational movement of the water inside the cylinder that becomes more intense as the difference between the two levels increases. This swirl, which is generated in the direction of rotation of the pump, causes a corresponding reduction of the pumping capacity, such that it always corresponds to the reduced volume of water to be pumped. In this manner, the pumping capacity of the pump can be regulated in a range from approximately 50% to 100%.
At full-load operation, however, this device has one disadvantage. As a result of the configuration of the device described above, there is a rotational motion of the water in the interior of the cylinder even when the pump is operating at full pumping capacity. This minimal residual swirl in the direction of rotation of the pump prevents the pump from achieving its maximum pumping capacity, and limits the maximum pumping capacity to values less than 100%.
Therefore, the object of the invention is to improve the maximum achievable pumping capacity of a pump in full-load operation.